The present invention relates to devices, systems, and methods for MRI-guided cryosurgery. More particularly, the present invention relates to a cryosurgery apparatus compatible for use within the magnetic environment of a functioning magnetic resonance imaging system and fully controllable by a surgeon positioned within that magnetic environment, wherein the cryosurgery apparatus is also optionally operable under algorithmic control, control decisions being based on information gleaned from MRI monitoring of a cryosurgery procedure in real time.
The present application relates to the use of cryosurgical tools in an MRI environment.
In the early days of magnetic resonance imaging, MRI was used only as a diagnostic tool. MRI imaging was used to visualize body tissues and to locate and evaluate problematic tissue structures. When MRI-assisted diagnosis identified problems correctable by non-invasive surgery, non-MRI imaging modalities (ultrasound, x-ray and fluoroscopy endoscopic and laparoscopic cameras, etc.) were typically used to monitor the surgical procedure in real time. More recently techniques have been developed to use MRI during surgery. Use of MRI in real time has major advantages for certain kinds of surgery, yet presents unique problems relating to the compatibility of equipment used within MRI's powerful magnetic environment. Use of magnetic resonance imaging presents particular advantages for monitoring of cryosurgery procedures, yet existing systems for MRI-compatible cryosurgery have significant limitations and disadvantages.
Cryoablation of tissues has become an increasingly popular method of treatment for a variety of pathological conditions. Malignancies in body organs such as the breast, prostate, kidney, liver, and other organs are successfully treated by cryoablation, and a variety of non-malignant pathological conditions, such as benign prostate hyperplasia, benign breast tumors, and similar growths are also well treated by cryoablation of unwanted tissues. Certain cases of intractable chronic pain ate also treatable through cryosurgery, by cryoablation of selected nervous tissue.
Cryoablation of pathological tissues or other unwanted tissues is most often accomplished by utilizing standard medical imaging modalities to identify and locate a locus for ablative treatment. Once a treatment locus has been identified and located, one or more cryoprobes are inserted into the selected locus, then cooled sufficiently to cause the tissues surrounding the treatment heads to reach cryoablation temperatures. Depending on the treatment protocol, tissues may be thawed and refrozen. Tissues thus treated loose their functional and structural integrity. Cancerous cells cease growing and multiplying, and cryoablated tumor tissue materials, whether from malignant tumors or from benign growths, lose their structural integrity and are subsequently sloughed off or absorbed by the body.
Cryoablation temperatures are temperatures at which cellular structure and functionality of tissues are reliably destroyed. In current practice cryoablation temperatures are generally taken to be in the approximate range of −40° C. and below, though of course final determination of appropriate cryoablation temperature is the responsibility of the surgeon in view of the particular circumstances of each clinical case.
When a cryoprobe is cooled to cryoablation temperatures, a volume of frozen tissue forms around the probe, commonly called an “iceball”. A cryoablation iceball contains a first volume of tissue, sometimes referred to herein as an “ablation volume”, which ablation volume is adjacent to the probe and cooled to cryoablation temperatures. The first (ablation) volume is surrounded by a second volume of tissue cooled to temperatures above cryoablation temperature but below the freezing point of water. Within the ablation volume cellular structure and function are reliably destroyed. Within the second volume, tissues are damaged to varying degrees, yet their structure and function are not reliably destroyed.
It is a major limitation of existing imaging modalities that they are unable to display to a surgeon the border separating those first and second volumes.
Arriving at a correct understanding of the position and three-dimensional shape of that border is of critical importance to a surgeon performing a cryoablation. If he underestimates the extent of the ablation volume, he destroys healthy tissue unnecessarily. If he overestimates the extent of the ablation volume, he risks failing to destroy dangerous functional pathological (e.g. malignant) tissue structures.
Lack of systems providing accurate information on the size and position of an actual cryoablation volume is a major unsolved problem of contemporary cryoablation technique.
Currently known non-MRI imaging modalities are not adjusted nor designed to directly image the size and position of an actual cryoablation volume. MRI imaging is capable of detecting and displaying tissue temperatures, yet no MRI system commercially available today is able to detect and display the borders of a cryoablation volume, because available MRI systems cannot detect and display temperatures within frozen tissue. Although MRI detection of temperatures within very cold temperature ranges appears to be theoretically possible, no MRI system commercially available today provides this capability.
Given the limitations of currently available techniques as described above, cryosurgeons are forced to estimate the position and size of the first (ablation) volume, based on available information, and in particular based on detected size and position of the second (frozen tissue) volume.
X-ray technologies, such as fluoroscopy, are capable of showing the borders of a frozen volume (the “iceball”), yet they show only a projected shadow of the iceball perpendicular to the main axis of the x-rays. Ultrasound clearly shows an external iceball border, but shows only the iceball border that is closest to the ultrasound probe. (That is, ultrasound shows only the portion of the border between frozen and non-frozen tissue which is situated between the frozen tissue and the ultrasound probe.) The opposite border is not visible in the ultrasound display. A plurality of synchronized ultrasound probes directed towards the iceball from various surrounding positions would provide better information, but such a solution has been found to be impractical in some cases and impossible in other cases. Thus, both ultrasound and x-ray technologies deliver only partial information concerning the size and position and three-dimensional shape of the iceball, and neither can deliver direct information concerning the size and position and three-dimensional shape of the cryoablation volume contained within the iceball boundaries.
For the purpose of understanding the size and position of an ablation volume, information provided by magnetic resonance imaging is superior to that available from x-ray and ultrasound imaging methods.
In the future, MRI systems may provide capability of direct imaging of an isotherm within frozen tissue, such as for example, the −40° C. isotherm which, according to current clinical thinking, marks the external border of the ablation volume.
Currently available MRI systems provide three other types of information which may be used to achieve accurate estimations of the position of that border.
First, a plurality of MRI ‘slices’ showing the border of frozen tissue, the external border of the iceball, permit to visualize the entire shape of the iceball as a whole and in detail, independent of any particular direction or point of view. Using known techniques, a plurality of such ‘slices’ may be combined algorithmically to create a solid model of the iceball in three dimensional space.
Second, MRI's ability to measure temperatures in non-frozen tissues permits to develop an appreciation of thermal gradients within tissues surrounding the iceball.
Third, MRI images can provide accurate information relating to the exact position of an operating cryoprobe within treated tissue. This information, together with temperature data available from sensors within the probe itself can contribute to estimation of temperature distribution within the frozen tissues.
These three abilities provide raw materials for accurate estimations of the size and position of an ablation volume concealed within a detectable iceball. Accurate estimation of the size and position of an ablation volume is critically important in cryosurgery, since it is generally a goal of cryosurgery to ablate all pathological tissue while destroying and damaging as little as possible of healthy tissue surrounding the pathological tissue. It is thus critically important that a surgeon, during a procedure, have a good and accurate understanding of what tissues he has frozen, and what tissues he has reliably killed. A surgeon who is unable to observe or accurately estimate the size and shape of an ablation volume is forced systematically underestimate the size of the ablation volume, at least when dealing with malignant or possibly malignant tumors, because total destruction of the entire tumor is essential to treatment, lest potentially lethal live cancer cells be left behind following surgery. A cryosurgeon lacking accurate means for observing or estimating the position of the borders of an ablation volume is forced to err on the side of caution, and to extend cryoablation well beyond the locus where ablation is actually needed and desired. He thereby avoids uncertainty about whether all portions of a lesion (e.g., a malignant tumor) have been reliably destroyed, but unfortunately destroys considerable healthy tissue along with the lesion whose ablation is desired.
Thus it is to be expected that a system rendering visible the border of an ablation volume, or alternatively a system facilitating accurate estimation of the size and position of such a border, would reduce hospital stays, decrease danger of surgical complications, speed recovery, and avoid various deleterious consequences to the long-term health and quality of life of the recovering patient.
For this and other reasons, practice of cryosurgery under real time MRI monitoring is highly desirable.
However, practice of cryosurgery under real-time MRI monitoring is difficult to accomplish. Several obstacles must be overcome.
The cryosurgical equipment must be such as to be substantially unaffected by the MRI system's powerful magnetic field. A cryoprobe constructed of non-MRI-compatible materials may be subjected to powerful undesired forces generated by magnetic interaction between the probe and the MRI magnetic field, and/or may distort the magnetic field and thereby create distortion of the MRI image. It has been found that cryoprobes and associated hardware constructed from materials such as titanium and inconel are not subjected to strong forces induced by magnetic fields of imaging equipment, and do not distort MRI images.
Electrical circuits used within the MRI environment must be shielded, lest they be subject to undesired induced currents generated within the electrical circuitry. Induced currents can lead to uncontrolled phenomena such as distorted data and/or distorted control signals.
Cryosurgery equipment for use within an MRI environment must also be such as not to cause distortion of the MRI's sensitive image-generating processes. Electric currents induced by an external magnetic field interacting with components of electronic circuitry could have such a distorting effect, as could electromagnetic radiation generated by the electrical circuitry during its normal operation. In particular, electronic circuits with switching components switching at high frequencies (e.g., computers) and with potential for broadcasting (intentionally or otherwise) electromagnetic fields generated thereby, must be shielded. Several layers of μ-metal (mu-metal) have been found to successfully isolate electronic circuits from MRI antenna.
Thus, cryosurgery equipment usable within an MRI environment must be made of MRI-compatible material, and electronic circuitry included in the cryosurgery equipment, if any, must be shielded by several layers of μ-metal or the equivalent. Preferably, MRI-compatible cryosurgery equipment should be as convenient, safe, and effective as ‘normal’ (non MRI compatible) cryosurgery equipment.
U.S. Pat. No. 5,978,697 to Maytal presents elements of an MRI-compatible cryosurgery system, and is here included by reference Maytal's system provides two modules and a set of connecting links between them.
A first module, referred to herein as an “inside” module, is for use inside an MRI “room” (that is, inside an MRI magnetic environment), and includes Joule-Thomson cryoprobes insertable in a patient during a cryosurgical intervention, which cryoprobes are operable to cool to cryoablation temperatures when supplied with high-pressure cooling gas, and further operable to heat, for disengagement from adhering frozen tissues, when supplied with high-pressure heating gas. The cryoprobes comprise simple control elements such as buttons operable by a surgeon, for passing from one phase of operation (e.g., cooling) to another phase of operation, (e.g., heating).
A second module, referred to herein as an “outside” module, is for use outside an MRI magnetic environment and is positioned away from the immediate environment of the operating surgeon. The outside module provides a support infrastructure for op cryoprobe and other equipment of the inside module.
The outside module stands outside the magnetic environment of the MRI system, and, is typically distanced from the immediate vicinity of the patient. The outside module includes a gas supply for supplying high pressure heating gas and high-pressure cooling gas, and has various manual and automatic valves for controlling gas flow. The outside module also has a user interface operable to display operating status of the cryoprobes and other equipment of the inside module, and is, further operable to accept commands from an operator. An operator interacting with the outside module can view information received, analyzed, and displayed by the outside module, which information is at least partially based on data from sensors within the inside module.
The operator interacting with the outside module can control operation of the outside module, and thereby (e.g., by controlling valves of the outside module which govern flow of high-pressure gasses to the inside module) thereby control functions of the inside module as well.
In the system taught by Maytal, inside module and outside module are linked by, gas supply lines and by electronic data transmission lines. Maytal teaches methods and configurations for providing such lines linking an inside and outside modules, including the method of providing a channel within the MRI magnet itself to accommodate gas and data lines linking inside and outside modules.
A major disadvantage of the configuration taught by Maytal is the described separation of control functions into inner and outer modules, which configuration provides user access to some control functions from within the inner module (e.g., control buttons selecting cooling or heating of cryoprobes), yet provides user access to other control functions from the outer module (e.g., manual control of gas valves, user interface for viewing a display reporting cryosurgery system status, etc.) In practice, systems conforming to the teachings of Maytal required two operators of the cryosurgical equipment, a first operator being a surge on, positioned within the magnetic field of the MRI equipment within an operating theatre environment, which first operator manipulates cryoprobes to perform the cryoablation, and a second operator who interacts with the user interface of the outer module, whose function includes inputting gas control commands and reporting orally to the surgeon, providing ongoing reports on cryosurgery system status which the surgeon, from his position near the patient, cannot see for himself and cannot directly control.
Maytal's system thus suffers from a serious disadvantage of inconvenience, in that it requires two operators, physically separated from one another, to operate the system, and in that the surgeon, in contact with a patient during the cryoablation does not have direct control over a variety of aspects of the cryoablation procedure. Maytal's system is further disadvantageous in that the separation of functions into two modules as described does not allow for combined or coordinated presentation of both of cryosurgery status data and of MRI imaging data within a common display interface.
Thus, there is a widely recognized need for, and it would be highly advantageous to have, an MRI-compatible cryosurgery system operable to provide direct control of cryosurgery components by an operating surgeon positioned within or near an MRI magnetic environment in a position convenient for operating on a patient, the system enabling real-time MRI monitoring of an on-going cryosurgery procedure.
There is further a widely recognized need for, and it would be highly advantageous to have, an apparatus for MRI-guided cryosurgery wherein display and control functions of the cryosurgery apparatus are integrated with display and control functions of the MRI apparatus, in a common display and with ergonomically compatible sets of controls for the two apparatus.
As stated above, currently available MRI systems do not provide direct information relating to size, position, and three-dimensional shape of the volume of total destruction (the ablation volume) created within an iceball during a cryoablation process. Yet such information would be of great use to a surgeon during a cryoablation procedure. Current MRI systems do not make recommendations to a surgeon during a cryoablation procedure, nor provide analyses specific to cryosurgical needs, nor do they automatically or partially automatically control the cryoablation procedure. Thus, there is a widely recognized need for, and it would be highly advantageous to have a cryosurgery system providing real-time recommendations to a surgeon during a cryosurgery procedure, and providing automatic or semi-automatic control of cryoablation equipment used in the body of a patient, based on algorithmic analyses of detected tissue configurations and of detected tissue temperature information gleaned from MRI image analysis.